1. Field of the Invention
The invention relates to imager technology. In particular, the invention relates to imager devices having a pixel with a transfer transistor gate configured to mitigate dark current generation.
2. Description of the Related Art
Exemplary CMOS imaging circuits, processing steps thereof, and detailed descriptions of the functions of various CMOS elements of an imaging circuit are described, for example, in U.S. Pat. No. 6,140,630, U.S. Pat. No. 6,376,868, U.S. Pat. No. 6,310,366, U.S. Pat. No. 6,326,652, U.S. Pat. No. 6,204,524, and U.S. Pat. No. 6,333,205, each assigned to Micron Technology, Inc. The disclosures of the forgoing patents are hereby incorporated by reference in their entirety.
FIG. 1 illustrates a top-down view of a conventional CMOS pixel 10 having a photodiode 14 in a substrate 12 as a photoconversion device. The pixel 10 includes a transfer transistor gate 16, which, with the photodiode 14 and a floating diffusion region 24, forms a transfer transistor. Also included is a reset transistor gate 18, which gates a reset voltage (Vaa) applied to an active area 26 to floating diffusion region 24 so that the floating diffusion region 24 resets. The photodiode 14 may also be reset when both the reset transistor gate 18 and transfer transistor gate 16 are turned on. Also included is a source follower transistor gate 20, which is electrically coupled 25 to the floating diffusion region 24 and which is part of a source follower transistor formed by active area 26, which is connected to voltage source (Vaa), and an active area 28 associated with a row select transistor gate 22. The row select transistor gate 22 is operated as part of a row select transistor, which connects active area 28 and active area 30, which is connected to the pixel output for reading the pixel.
As is shown in FIG. 1, in the conventional pixel 10, the transfer transistor gate 16 spans the photodiode 14. The pixel's 10 active regions, which include the photodiode 14, the floating diffusion region 24, and active areas 26, 28, and 30, are surrounded by a shallow trench isolation (STI) region 40. Where the transfer transistor gate 16 extends beyond the photodiode 14, it overlaps the edges of the STI region 40. This overlap can result in the production of dark current, which is undesirable in imager devices.